1. Field of the Invention
The present invention generally relates to a process that selectively polymerizes ethylene in the presence of an alpha-olefin, and a precatalyst and catalyst useful in such process.
2. Description of the Related Art
Polyolefins that are polyethylene polymer (also known as polyethene or poly(methylene)) and poly(ethylene alpha-olefin) copolymers are types of polyolefins (also known as polyalkenes) widely used in industry. They are desirable for making, for example, containers, tubing, films and sheets for packaging, and synthetic lubricants. One subtype of polyethylene is a high density polyethylene (HDPE).
A particularly valuable subtype of poly(ethylene alpha-olefin) copolymer is a poly(ethylene alpha-olefin) block copolymer or, simply, an olefin block copolymer (OBC). OBCs are characterized as having at least one so-called “hard segment” or block comprising residuals of ethylene monomer and at least one so-called “soft segment” or block comprising residuals of an alpha-olefin (also known as an alpha-olefin and 1-olefin) monomer. OBCs are available from The Dow Chemical Company, Midland, Mich., USA under the trade name INFUSE™ Olefin Block Copolymers. INFUSE™ Olefin Block Copolymers are useful in a variety of forms and applications such as, for example, those listed at www.dow.com/infuse. Part of a preparation of an OBC involves a process that, among other steps, selectively polymerizes ethylene in the presence of the alpha-olefin to form the one or more hard segments of the OBC.
U.S. Pat. No. 6,114,481 mentions a method of and catalyst system for polymerizing olefins to prepare olefin-derived copolymers. The catalyst system contains an organometallic complex of a Group 4 metal and an activator. The organometallic complex contains a ketimide ligand (i.e., (Sub 1)(Sub 2)C═N—).
Adams N., et al., Discovery and evaluation of highly active imidotitanium ethylene polymerization catalysts using high throughput catalyst screening, Chemical Communications, 2004: 434-435, mention a method of and catalyst system for polymerizing ethylene to prepare polyethylenes. The catalyst system contains an organometallic complex of the Group 4 metal titanium and an activator. Some of the organometallic complexes contain a single ketimide ligand (i.e., (R)2C═N—).
PCT International Patent Application Publication Number WO 2005/123790 A1 mentions a method of and catalyst system for polymerizing olefins to prepare olefin-derived copolymers. The catalyst system contains a catalyst covalently bonded to an activator.
Chemical industry desires new processes and catalysts for selectively polymerizing ethylene in the presence of an alpha-olefin.